Most likely no one will confuse you for the groom, whatever you wear. Should you choose a white DJ,the groom will probably have some accessories that will differentiate him from you, like a bride, and some sort of foliage on his lapel. Best course of action would be to ask him if he (meaning the bride) prefers to be the only one in white DJ. A midnight or black rig would give you more mileage than a white jacket naturally, though do take care to get proper midnight blue, not some 007 movie poster blue. Black is easier to source.
The betrothed sets the dress code, if you upstage the groom by honouring it, you're hardly at fault (some may disagree). As for the common folk, your only concern is what the female portion thinks. So go all in.Edited by AdductorMagnus - 4/8/16 at 4:37pm

Gentlemen, I'm a bit of a planner so I'm asking about a wedding I've been invited to coming up in July. Here's the dilemma:
1. It's in Jacksonville, Florida.
2. It's in July.
3. The ceremony is at 4:30 pm
4. It's "black tie optional"

Definitely wear a tux. In this case, I'd go with a cream, shawl collar jacket. No one will confuse you with the groom.

I do not currently own a tux, but could commission one from a tailor to be sent to me based upon past measurements. However, this is at 4:30.. Isn't that a little taboo? Also, I'm really not that sure how many people will actually be wearing tuxedos...

Cheers to those of you that take the time to weigh in..

EDIT: It's a gigantic Lebanese wedding at the Basilica of the Immaculate Conception Cathedral followed by the reception at TPC Sawgrass (PGA Headquarters) country club and golf course. There'll be babes a plenty and I want to look damn good without melting.

Technically, black tie events should take place after 6:00. I'd be okay wearing a tuxedo to something that starts at 4:30, though, as the reception will most likely be starting after 6:00 and it is probably not practical to change between the ceremony and reception (plus nobody does it these days (not a good reason really, but it is a fact)). I'm also a bit biased as I own a tuxedo and like to wear it, so I'll do it if it is at all reasonable. Put black tie optional on a wedding invitation and have a ceremony that starts after 4:00 and I'm sold.

As far as your question below about midnight blue, it's perfectly acceptable for a tuxedo, but it will be noticed (most likely in a good way). I went with black for my first tuxedo because I wanted to be as conservative and nondescript as possible, but if I get a second tuxedo, it will be midnight blue.

Definitely wear a tux. In this case, I'd go with a cream, shawl collar jacket. No one will confuse you with the groom.

Lebanese babes. You lucky sunavabich.

I love the idea of a cream dinner jacket, but wouldn't do it before owning a regular black or midnight blue dinner jacket that can be worn outside of summer. Of course, one could always get both in the true spirit of SF.

Basically @Dako, you can't go wrong. Go get the tux of your dreams, and rock it at the wedding. But we'll want picks of the ladies! And maybe one of your tux too.

What's your budget?

I'll probably go through a tailor in Bangkok I've worked with in the past (Tailor on Ten). The only reservation I have is choosing a dark navy fabric without holding it in my hand. The benefit here is of course price - I can have something half canvassed and made to measure with great milled fabrics for as low as $550.

I cringe at buying something off the rack but I guess it isn't totally out of the question.. All in all I'm trying to spend less than $800 or so. Recommendations? Ideas?

So, I'm getting married in morning dress, as pictured in my earlier post. 1500 ceremony, followed by a short Danube river cruise before the reception at 1800. The plan was to change into black-tie for the reception, but then again you only get married twice, statistically. So, I perused E & Bay et al, and happened upon an evening tailcoat, or queue de pie as it was listed on the French eBay site (I love Google translate). It fit reasonably well, a smidgen tight in the shoulders, but I think I'll live. Now, the problem is finding a fitting waistcoat. My trousers are cut for braces, fishtail and all, 14" rise. Single "fancy braid" stripe, which you'll just have to forgive me. Coat measures 20" from top of shoulder to point when worn. I measure 18“ from top of shirt shoulder to waistband. My question is, would a waistcoat panel length of 19-20" be right? When worn, is the top of the panel at the top of the shoulder? I'd like to avoid making a bum purchase where the waistcoat peaks way out under the cutaway, or leaves a gap over the waistband. Having one made is not an option financially, I'm already way over budget...

Oh, pics
Yeah, taking pics in the mirror oneself is less than ideal.
Tails end behind the knee, so a tad too short? Also, a bit of waistband barely shows in the corner of the cutaway by the lateral brace-button, so I fear a touch of white is unavoidable. I guess this was made for someone a bit shorter than me.
Thoughts? Sell this and stick with black-tie, or could this be serviceable?

I don't think you need to sell it. You just need to find a proper waistcoat. I don't think your waistcoat will show underneath the tailcoat. It's a bit hard to tell from the photos, but I get the impression that it will work. I am judging based on the third picture from the top. The coat point appears to extend well over the waistband of the trousers. May I recommend shortening the sleeves though? They look too long in pictures two and three.

I don't think you need to sell it. You just need to find a proper waistcoat. I don't think your waistcoat will show underneath the tailcoat. It's a bit hard to tell from the photos, but I get the impression that it will work. I am judging based on the third picture from the top. The coat point appears to extend well over the waistband of the trousers. May I recommend shortening the sleeves though? They look too long in pictures two and three.

Agreed, sleeves are on the to-do list.

The points extend over the waistband, absolutely. But the angles on the sides where cutaway meets tails doesn't, so a waistcoat covering the waistband will show a little there. I've scoured vintage shops for waistcoats here in Budapest, Hungary to no avail. Found a few sets of tails though, 4-8 sizes too small, but it seems few waistcoats have survived the soviet era.

As I've never even seen proper full dress in person, I have no idea how the waistcoat is worn, as in where the adjustable neckband should end and the marcella panels begin in the shoulder area. I've asked for length measurements on a couple of waistcoats on eBay in my chest-size, but buying this item online is a daunting task I'd like to get right on the first go.